Liquid coffee, and liquid coffee concentrates, are increasingly in demand for commercial and/or industrial purposes. The production and sales of liquid coffee, e.g. liquid coffee concentrates for use in coffee dispensing machines, makes it desirable to provide liquid coffee that has a sufficient shelf-life. Up to now, such liquid coffee products are mostly available in a frozen form, and sometimes refrigerated. Non-refrigerated storage would decrease supply chain costs. However, any products sold for non-refrigerated storage still have an undesirably short shelf-life.
Generally speaking, a liquid coffee (such as a concentrate or an extract) is unstable over time and becomes increasingly acidic at room temperature. As is known by the skilled man, the pH drop might be due to microbial action and to chemical reaction, such as a slow hydrolysis reaction of some compounds such as esters and lactones, oxidation of carbonyl group containing compounds or even the Maillard reaction occurring among polysaccharides and proteins. A pH of 4.8 is commonly considered in literature as the lower limit for taste acceptability. Below that pH level the coffee extract becomes undrinkable.
To overcome microbial acidification the liquid coffee is often treated by UHT (Ultra High Temperature). Particularly suitable UHT treatment is at 120° C. for a couple of seconds.
A reference addressing the chemical acidification is US 2010/0316784. Therein a treatment is proposed comprising adding an edible alkali source to a liquid coffee concentrate. This serves to artificially increase pH. Before or after the addition of alkali, a heat treatment is conducted so as to artificially drive acid-generation reactions in the coffee concentrate to completion. More particularly, the heat treatment is conducted between 140 and 146° C. at a holding time of at most 3 minutes. This method fails, however, to produce products of sufficient shelf-life and quality.
Another drawback of the aforementioned process is the addition of alkali. In many jurisdictions, such an addition is considered undesired and/or the resulting product is no longer entitled to be called a “coffee”, like under the EC food regulations. It would be desirable to develop a process for making liquid coffee whereby the addition of ingredients other than those obtained from a coffee extract itself is unnecessary, and yet provide a storage stable liquid coffee concentrate of good flavor qualities.
Another reference addressing the stabilization of liquid coffee by treatment with alkali is EP 861 596. Herein a coffee extract is treated with an alkali, which is present in an amount effective to convert acid precursors present in the coffee extract to their respective acid salts, and thereafter neutralizing the treated coffee extract with an acid, in an amount sufficient to neutralize any excess alkali from the first step. Apart from the aforementioned drawback of using alkali, this method also adds acid, which increases the amount of foreign components present in the liquid coffee. Moreover, the method is essentially based on introducing ionic substances (salts) which are prone to adversely affect taste.
Yet another reference addressing shelf life of liquid coffees is EP 1 374 690. Herein a coffee extract is subjected, essentially immediately after preparation, to correction of acidity by the addition of a base or an anion resin. The resulting extract is subjected to pasteurisation. The pasteurisation is discussed with reference to holding times and temperatures that do not affect the organoleptic properties of the coffee extract. A typical temperature range is 100° C.-140° C. at a holding time of at most 1 minute. This method fails also to produce products of sufficient shelf-life and quality.
The object of the present invention is to provide a process with which an improvement of the quality of the coffee concentrate is obtained in storage stability as well as in flavor.